As optical communication grows, there is a need for the systems that transmit the signals to grow in capacity. To this end, there is increasing resort to WDM optical networks using optical fibers as the waveguides for transmission. In WDM systems, there is a need to provide at nodes in such systems ADMs that selectively remove one or more channels whose signals are addressed to such nodes and to replace them with new channels originating at such nodes, typically of the same wavelengths as the wavelengths of the dropped channels.
It is important for an optical network to compete successfully in a competitive environment that its ADMs be reliable, rugged, and of low cost.
It is also important that residual leakage of the dropped channels be very small to minimize their interference with the added channels of the same wavelength. This requires low channel crosstalk through the wavelength multiplexers and demultiplexers and high-contrast optical switches that are used in optical networks.
It is also important that the adding and dropping of the channels be done conveniently with little disturbance of the channels being retained.
A variety of apparatus for multiplexing and demultiplexing of optical signals is available for use in the invention. Of special interest are arrayed waveguide grating routers (AWGR) that have proven very adaptable for use in multiplexing and demultiplexing channels. AWGRs comprise a pair of free space planar components, such as star couplers, that are interconnected by a grating composed of an array of waveguide stripes whose lengths differ by prescribed amounts and that are supported on a planar substrate.